An ignition system is described in German Disclosure Document DE-OS 2,503,899 in which a timing signal for determining the ignition time is derived from the passage through zero of the above-mentioned control signal. In the prior art systems, as well as in the present invention, the ignition system comprises a spark plug which is connected in series with the secondary winding of an ignition coil. The primary winding of the ignition coil is connected in series with an ignition switch. During the time the ignition switch is closed, energy builds up in the ignition coil which, when the switch is opened, is transferred to the spark then created in the spark plug. The basic problem for these circuits is to cause the ignition switch to close at a time instant prior to the actual ignition which allows sufficient energy to be stored in the coil to result in an adequate spark. Further, the prior art systems can be divided into two classes namely those in which only one spark is furnished at the desired ignition time and those in which a series of sparks is furnished at this time. For the latter, it is also required that adequate current for the subsequent sparks will flow at the time each subsequent spark is ignited. Systems are known in which a current measuring system is connected to the ignition switch and the current is interrupted by opening of the switch when it is determined that the amplitude of the current is such that sufficient energy is stored in the coil. Such a current measuring system is disclosed in for a single spark system and in U.S. application Ser. No. 734,745, filed Oct. 22, 1976, JUNDT et al, now U.S. Pat. No. 4,176,645, to which German Disclosure Document DE-OS 2,549,586 corresponds U.S. Pat. No. 4,083,347, Grather and Rabus, to which German Disclosure Document DE-OS 2,606,890 corresponds for a multiple spark system. Basically the problem can be solved in two ways. Either the spark is ignited when the current has the correct value as mentioned above, which can lead to an ignition at other than the actual desired ignition time, or the ignition can take place at the exact ignition time but the current may then not have the desired amplitude. In the known systems, the ignition time is the time at which the above-mentioned control signal passes through zero. If now the ignition switch is closed when the control signal has a predetermined slope or a predetermined amplitude prior to passing through zero, then adequate results can only be obtained at higher speeds since the shape of the curve of the control signal is sufficiently stable and defined only at these higher speeds. At lower speeds, the control signal varies so much that large variations in the closing time of the ignition switch result.